SQL Churn After First Month | Dataford Interview Questions

Given two tables (users and transactions), write a query to identify users who churned after their first month.

Treat a user's first month as the calendar month containing their earliest non-null transaction date. A user churns when they have no transaction in the immediately following calendar month.

Output

One row per churned user with user_id, user_name, and first_month.
Order by first_month ascending, then user_id ascending.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
user_name	VARCHAR(100)	User display name

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
user_id	INT	User associated with the transaction
transaction_date	DATE	Date the transaction occurred

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